1. Field of the Invention
The invention generally relates to cervical ripening devices and methods.
2. Description of the Relevant Art
Cervical ripening refers to the effacement or thinning of the cervix followed by dilation in preparation for the birthing process. Critical factors in the initiation of the ripening process include release of enzymes, hormonal factors, and local pressure on the internal os of the cervix as a result of the fetus' head following decent. When the progression of cervical ripening is slow or is not naturally initiated, stimulation by insertion and inflation of a balloon catheter to apply additional local has been shown to be effective.
Current methodology utilizes a Foley urinary catheter that is inserted into the cervical os and inflated to 50 to 80 ml with saline solution. The resulting spherical balloon is 5 to 6 cm in diameter. The area in contact with the internal os is roughly 30 to 45 cm2 with the locally applied pressure a function of the cosine of the angle between the axis of the cervical channel and the point of contact by the balloon. The addition of approximately 1 Kg to the distal end of the Foley catheter has improved the ripening process substantially.
Several problems with the Foley catheter approach to cervical ripening are evident. Since the balloon is spherical, local pressure is not uniform over the internal os. This presents the potentiality that local release of hormonal and enzymatic factors are not uniformly induced in the cervix, thus, sub-optimally facilitating cervical ripening. Only the lower hemisphere of the balloon that is prescribed by the bisection of the catheter balloon by a plane perpendicular to the catheter axis is in contact with the internal os. The upper hemisphere protrudes in to the uterus potentially applying elevated pressure to the head of the fetus. The tip of the Foley catheter presents addition protrusion in to the uterus potentially injuring the fetus. The added kilogram of weight is generally a liter bag of saline solution which is allowed to hang over the side of the bed. Significant discomforts to the patient and the potential of injury from inadvertent snagging of the bag are added complications with this method.